Navigation:  Step-By-Step Examples > Example 18: Response Spectrum Analysis of a Beam

Problem Description

A simply supported beam (L = 20 ft) [Ref 24, Problem.4.8] is subjected to a response spectrum in the vertical direction at both supports. The beam section is of size 1.458 in x 14 in.

 

Material: E = 30 e6 psi, density = 6538.08 lb/ft^3

 

Damping: 0.0

Spectrum Definition:

 

 

Suggested Modeling Steps

▪Set proper units from Settings and Tools > Units & Precisions.  

 

 

▪Define the material from Modify > Member Properties > Materials

 

▪Define the section from Modify > Member Properties > Sections using the Regular Section button.  

 

 

▪Define the two nodes from Tables > Nodes.  

 

 

▪Define the one beam from Tables > Members. Make sure the correct material and section are used for this beam.

 

 

▪Select the beam we just created. Use Modify > Split > Split Members to split it to 10 elements of equal lengths.

 

 

▪Use Create > Boundary Conditions > Support to assign supports to node 1 and 2

 

 

 

▪From Create > Generate Loads > Response Spectra Library > Add, define the spectrum.

 

 

 

▪We will convert self-weight to calculate masses. So from Create > Draw Loads > Self Weights, define the self-weight multiplier as -1 in Global Y direction.  By default, self weight will be of load case “Default”, which is included in the default load combination “Default”.

 

 

 

▪Set structural model as 2D Frame from Analysis > Analysis Options. We will not consider shear deformation on members.

 

 

▪Frequency analysis must be run prior to response spectrum analysis.  So run frequency analysis from Analysis > Frequency Analysis. We will compute the first 10 modes.

 

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▪Run response spectrum analysis from Analysis > Response Spectrum Analysis.  Make sure we use the correct spectrum and apply directional factor only in Y direction.

 

 

▪After the response spectrum analysis is done, we can then exam results such as Analysis Results > Dynamics > Eigenvalues, Analysis Results > Dynamics > Modal Nodal Displacements, Analysis Results > Dynamics > Modal Member End Forces & Moments, etc.

 

The following is a result comparison between ENERCALC 3D and the reference [Ref 24].